Installation of filter capacitors into feedthroughs for implantable medical devices

ABSTRACT

A feedthrough device and brazing process for joining the constituent parts of the feedthrough device, while allowing a lead to pass therethrough in a nonconductive manner. The feedthrough comprises at least one lead, a ferrule defining a capacitor recess and defining an insulator recess, an insulator disposed in the insulator recess of the ferrule, the insulator defining a passageway sized to allow the lead to pass therethrough. The feedthrough further comprises a capacitor disposed in the capacitor recess and defining a capacitor passageway sized to allow the lead to pass threrethrough, and the capacitor comprises first and second sets of plates, wherein the first set of plates is conductively coupled to the ferrule and the second set of plates is conductively coupled to the lead. Brazing is a two step process wherein the braze joints between the insulator and the lead and between the insulator and ferrule are formed first at a first temperature using an insulator braze material. The second step of brazing is performed at a lower temperature than the brazing in the first step, and utilizes capacitor braze materials that are different from the insulator braze materials in that they have lower melting temperatures than the insulator braze materials.

BACKGROUND

[0001] This invention relates to feedthroughs for providing anelectrical path for implantable medical devices including electricalpulse generators. Examples of such devices are implantable cardiacpacemakers and implantable cardiac defibrillators for correction ofcardiac abnormalities. The pacemaker or defibrillator device has ahousing containing a pulse generator including associated circuitry anda battery that serves as a power supply. A conductive lead or pinextends from the pulse generator circuit in the interior of the deviceand passes through the device housing where it is connected via amedical lead to an electrode surgically attached to an appropriatelocation in the heart.

[0002] One of the concerns related to the use of such implantablemedical devices (pacemakers, defibrillators, etc.) is that they aresubject to stray electromagnetic interference (EMI). Such EMI may comefrom sources such as television transmitters, cell phones, theftdetection devices and so on. This spurious EMI is highly undesirablebecause it can interfere with proper functioning of the implantedmedical device, either by inhibiting a proper response or by causing animproper one. Such stray EMI can essentially be eliminated as a problemsource by shunting the EMI to ground with the use of a filter capacitorconnected between the input lead wire(s) and electrical ground.Typically, one capacitor is positioned between each such lead wire andground. These capacitors are often built into a monolithic structure orarray when used for a multilead feedthrough. If the array is in the formof a right circular cylinder, it is designated a discoidal capacitor.

[0003] However, these prior art type feedthroughs routinely useconductive polymeric materials such as polyimides and epoxies ormetallic materials such as solder alloys for holding their constituentparts together. Use of the conductive polymeric materials requires carein preventing leakage of the conductive polymer into locations in theassembly where it could cause a short circuit rendering the implantablemedical device inoperative. In addition, conductive polymers exhibitrelatively low electrical conductivity as compared with metallicmaterials. The bonding mechanism between the conductive polymer and themetallic members of the feedthrough is predominately mechanical,resulting in a relatively weak electrical and mechanical connection.Solders have relatively low melting temperatures such that subsequenthigh temperature welding operations on other parts of the device cancompromise the soldered joint or cause beading in which a ball or pelletof solder could fall into a location in the device where a short circuitcould result. Additionally, some soldering operations require the use offluxes that leave behind undesirable residues after the soldering iscompleted, that can be a source of entrapped moisture, possiblyresulting in device failure. Thus, there is a need for a better filteredfeedthrough device as well as a better filtered feedthrough assemblyprocess.

SUMMARY

[0004] The present invention provides a feedthrough assembly and amethod of making the same wherein capacitive arrays are installed into asingle or multi-pin feedthroughs using a brazing process. The brazematerial serves to join the capacitor to the feedthrough, holding itsecurely in place. In addition, the braze material provides theelectrical connection from one set(s) of internal capacitor plates tothe flange or ferrule and from the opposing set(s) of plates to thefeedthrough lead wire(s).

[0005] In particular, the feedthrough comprises a lead or conductivepin, a ferrule defining a capacitor receiving recess and an insulatorreceiving recess, a capacitor disposed in the capacitor receiving recessand defining a capacitor passageway for the lead to pass therethrough,and an insulator disposed in the insulator receiving recess and definingan insulator passageway for the lead to pass through. The lead or pinpasses through the insulator in a nonconductive manner. The capacitorcomprises first and second sets of plates separated by a dielectric, thefirst set of plates being conductively coupled to the ferrule and thesecond set of plates being conductively coupled to the lead so that thelead or pin passes through the ferrule in a non-contacting andnonconductive manner. An insulator braze material is used for formingthe insulator-lead braze joint and the insulator-ferrule braze joint. Acapacitor braze material is used for forming the capacitor-ferrule brazejoint and the capacitor-lead braze joint.

[0006] The insulator braze material is typically gold, while thecapacitor braze material is a composition selected to be compatible withthe termination materials used in the capacitor. The brazing process isa two step procedure wherein the first step calls for the brazing of theinsulator-lead braze joint and the insulator-ferrule braze joint at afirst temperature using a selected insulator braze material. The secondstep of brazing calls for brazing the capacitor-ferrule braze joint andthe capacitor-lead braze joint, with the selected capacitor brazematerial at a second temperature that is lower than the firsttemperature. The braze materials for each step described in the detaileddescription. This second brazing process does not damage, weaken, orotherwise destroy the insulator-ferrule braze joint or insulator-leadbraze joint formed in the previous operation (first step of the brazingprocess) because if is performed at a lower temperature.

[0007] A durable feedthrough assembly is thus provided that is superiorto the prior art because the feedthrough can withstand subsequentwelding processes without losing its integrity and because theconstituent parts of the feedthrough are brazed together. If a solderwere used, it might melt, weaken, and bead up at the increasedtemperatures encountered during welding and a compromised joint couldthus result. Furthermore, beads of solder could form if soldering wereemployed and they could fall into the region of the implantable devicecontaining the electrical components causing short circuits and otherproblems. The present invention avoids these problems and thussuccessfully overcomes problems associated with the prior art.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008]FIG. 1 shows a side elevational full cutaway view of thefeedthrough device of the invention.

[0009]FIG. 2 shows a side elevational full cutaway view the same as FIG.1 that further illustrates the feedthrough device of the invention.

[0010]FIG. 3 shows a side elevational full cutaway view of analternative embodiment of the feedthrough device of the invention.

[0011]FIG. 4 shows a side elevational full cutaway view of analternative embodiment of the feedthrough device comprising a pluralityof leads.

DETAILED DESCRIPTION

[0012] Turning first to FIG. 1, the invention provides for a novelfiltered feedthrough device or assembly 20 (hereinafter feedthrough 20)that incorporates braze joints for installing one or more capacitors 22in a ferrule 24 of the feedthrough 20. The constituent parts of thefeedthrough 20 are first described in detail, these parts comprising theferrule 24, the capacitor 22, an insulator 28, and a conductive leadwire or conductive pin 30 (hereinafter lead 30). Then theinsulator-ferrule braze joint 82, the insulator-lead braze joint 80, thecapacitor-ferrule braze joint 90 and the capacitor-lead braze joint 92are described in detail. Ferrule 24 may be welded or otherwise joined tothe housing 32 of an implantable medical device such as an implantablecardiac pacemaker or an implantable cardiac defibrillator. Thefeedthrough 20 is for allowing the conductive lead 30 to pass from theinterior 32B of the housing 32 to the exterior 32A of the housing 32 ina nonconductive manner, i.e., electrically insulated from the housing 32that is typically embodied as a metal such as titanium.

[0013] The lead or pin 30 comprises an external portion 34, afeedthrough portion 36, and an internal portion 38, and may be embodiedas having a cylindrical shape with a diameter designated 30A. The lead30 is constructed of a conductive material such as platinum-iridiumalloys, niobium, or pure platinum so that it can carry the electricalimpulses from the pulse generator (not shown) within the housing 32 toelectrodes attached to the heart (not shown), in a manner well known tothose skilled in the art.

[0014] The ferrule 24, also constructed of metal, is embodied as acylindrical structure having a cylindrical exterior sidewall 44 and hasan insulator end 46 and a capacitor end 48. The ferrule 24 furthercomprises an insulator receiving recess 50 having a diameter designated50A in FIGS. 1 and 2, and a capacitor receiving recess 52 having adiameter designated 52A in FIG. 2. It is noted that while the figuresshow the insulator receiving recess 50 and the capacitor receivingrecess 52 as cylindrically shaped, these recesses may be embodied inother shapes, for example rectangular shaped recesses to accommodaterectangular shaped capacitors and insulators.

[0015] The insulator 28 has a cylindrical exterior surface 58 and may bemade of ceramics and other insulating materials well known to those ofordinary skill in the art. The insulator 28 has a diameter designated 62in FIG. 2, and it has an insulator passageway 64 extending therethrough,as seen in FIG. 2. The insulator passageway 64 has a diameter designated64A (FIG. 2) that is greater than the diameter of the lead designated30A (FIG. 2), so that the lead 30 is receivable in and can pass throughthe insulator passageway 64.

[0016] The insulator 28 also has a ferrule end 68 and an exposed end 70.The diameter of the insulator, designated 62 in FIG. 2, is less than thediameter designated 50A of the insulator receiving recess 50 in theferrule 24, so that the ferrule end 68 of the insulator 28 is receivablein the insulator receiving recess 50 in the ferrule 24. As will bedescribed presently, a brazing process according to the invention usingan insulator braze material 100 joins the insulator 28 to the ferrule 24and the lead 30 to the insulator 28.

[0017] At the capacitor end 48 of the ferrule 24 is the capacitorreceiving recess 52 having a diameter designated 52A in FIG. 2. Thecapacitor 22, may be embodied as a discoidal shaped capacitor and has acapacitor diameter designated 72 in FIG. 2. The cylindrical (discoidal)shaped capacitor 22 further defines a capacitor passageway 74 extendingtherethrough. The capacitor 22 may comprise first and second sets ofmetal plates 120, 130 separated by a dielectric 125 and be made to storecharge and filter undesirable EMI as shown in FIG. 2. A capacitor 22 ofthis type is well known to those skilled in the art. The capacitorpassageway 74 has a diameter greater than the lead 30 diameter 30A, sothat the lead 30 may pass therethrough. The diameter of the capacitor 72is such that it is less than diameter of the capacitor receiving recess52A in FIG. 2, so that the capacitor 22 is receivable in the capacitorreceiving recess 52 of the ferrule 24. It is noted that capacitor 22 maybe embodied such that it is completely received in the capacitorreceiving recess 52, or only partly received in the capacitor receivingrecess 52, or the ferrule 24 may be embodied such that it completely orpartly receives the capacitor 22 therein.

[0018] The capacitor passageway 74 has an internal surface 76 providedwith a metallized internal surface layer 76A. The capacitor 22 furthercomprises an exterior capacitor surface 78 about its circumference thatalso has a metallized external surface layer indicated by referencenumber 78A. As described above the capacitor 22 may comprise first andsecond sets of metal plates 120, 130 respectively shown in FIG. 2. Thesecond set of metal plates 130 makes contact with the metallizedinternal surface layer 76A, and the first set of plates 120 makescontact with the metallized external surface layer 78A of the capacitor22. The first and second sets of plates 120,130 may be of metal andseparated by layers of a dielectric material, such capacitors andconfigurations being well known to those to those skilled in the art.Indeed, the plates 120,130 and dielectric 125 may be made of a pluralityof different materials having the requisite properties to filterundesirable EMI, such capacitors being well known to those skilled inthe art.

[0019] The assembly of the feedthrough 20 will now be described followedby a description of the brazing processes. The brazing of thefeedthrough 20 is actually a two step process. In the first step, theferrule end 68 of the insulator 28 is inserted into the insulatorreceiving recess 50 in the ferrule 24 and brazed thereto using aninsulator braze material 100. Since the insulator diameter designated 62is less than the diameter of the insulator receiving recess designated50A, there is room between the exterior cylindrical surface 58 of theinsulator 28 and the insulator receiving recess sidewall 50B in theferrule 24, and that allows for the smooth insertion of the insulator 28therein. The lead 30, because it has a diameter designated 30A that isless than the diameter designated 64A (FIG. 2) of the insulatorpassageway 64, is fitted into and passed through the insulatorpassageway 64. The lead 30 is also brazed to the insulator 28 in thefirst step using the insulator braze material 100.

[0020] In such a configuration and as seen in FIG. 1, an insulator-leadbraze joint 80 (generated in a manner described below), is formedbetween the insulator 28 and the lead 30. The insulator-lead braze joint80 extends annularly about the circumference of the exposed end 70 ofthe insulator 28 and the lead 30, and the insulator-lead braze joint 80contacts the lead 30 and insulator 28 joining the lead 30 and theinsulator 28. Also, an insulator-ferrule braze joint 82 (generated in amanner described presently) is formed between the insulator 28 and theferrule 24, also seen in FIG. 1. The insulator-ferrule braze joint 82extends about the circumference of the insulator 28 at the point wherethe insulator 28 enters the insulator receiving recess 50 in the ferrule24. The insulator braze material 100 used for the insulator-lead brazejoint 80 and the insulator-ferrule braze joint 82 is the same.

[0021] In the second step, a capacitor braze material 102 is utilized tojoin the metallized external surface layer 78A of the of the capacitor22 to the interior sidewall 52B of the capacitor receiving recess 52,and to join the metallized internal surface layer 76A of the capacitorpassageway 74 to the lead 30. The second step thus forms thecapacitor-ferrule braze joint 90 and the capacitor-lead braze joint 92using the capacitor braze material 102.

[0022] Brazing (braze welding) may be employed to accomplish the brazingof the insulator-lead braze joint 80 and the insulator-ferrule brazejoint 82. The technique for brazing each of these described presently.The insulator-lead braze joint 80 and the insulator-ferrule braze joint82 may be formed by brazing techniques well known to those skilled inthe art, for example by placing the insulator braze material 100 at thelocation where the braze joint is to be formed and then applying heat tothe insulator braze material 100 at a temperature sufficient to form thejoint. Then, upon cooling, the insulator-lead braze joint 80 and theinsulator-ferrule braze joint 82, made of the insulator braze material100, form a hermetic seal between the lead 30 and the insulator 28 andbetween the insulator 28 and the ferrule 24.

[0023] The insulator braze materials 100 used for brazing theinsulator-ferrule braze joint 82 and for brazing the insulator-leadbraze joint 80 comprise:

[0024] pure gold;

[0025] gold alloys comprising at least one of tin, copper, silver,palladium, indium, titanium, niobium, vanadium, nickel, molybdenum,platinum;

[0026] silver;

[0027] silver alloys containing at least one of gallium, palladium, andaluminum; and

[0028] copper silver alloys that may contain tin, indium, palladium,nickel, gallium, palladium, and titanium.

[0029] As described presently, the above-described insulator brazematerial 100 used for the insulator-ferrule braze joint 82 and theinsulator-lead braze joint 80 are different from the capacitor brazematerial 102 used in forming the capacitor-ferrule braze joint 90 andcapacitor-lead braze joint 92, in that the capacitor braze material 102has a lower liquidus.

[0030] The capacitor braze materials 102 that may be used for brazingthe capacitor-ferrule braze joint 90 and the capacitor-lead braze joint92 comprise:

[0031] seventy-two percent silver and twenty-eight percent copper;

[0032] copper and silver and at least one of the following elements:titanium, indium, manganese, gallium, palladium, platinum, nickel ortin, so long as they are compatible with the capacitor 22 terminationmaterials; silver-germanium alloys;

[0033] gold alloys; and

[0034] and silver-palladium-gallium alloys so long as these materialsare compatible with capacitor termination materials.

[0035] To facilitate brazing of the capacitor-ferrule braze joint 90 andthe capacitor-lead braze joint 92 a thread-type preform (not shown inthe figures) of capacitor braze material 102 may be threaded onto thelead 30, and an annular shaped capacitor preform (not shown in thefigures), of capacitor braze material 102, having a diametersubstantially the same as the capacitor diameter designated 72 maypositioned about the exterior capacitor surface 78. The capacitor brazematerial 102 for the thread-type preform and capacitor preform isselected from the above described brazes for the capacitor-ferrule brazejoint 90 and capacitor-lead braze joint 92. Upon brazing, the annularshaped capacitor preform melts and the capacitor braze material 102seeps into or is drawn into the space between the exterior capacitorsurface 78 and the interior sidewall 52B of the ferrule 24, and thethread-type preform melts and seeps into the space between the lead 30and metallized internal surface layer 76A of the capacitor passageway74.

[0036] Brazing Process

[0037] The following example is an embodiment of the brazing processthat is itself a two step procedure, wherein the first step provides forforming the ferrule-insulator braze joint 82 and the insulator-leadbraze joint 80 (hereinafter braze joints 80,82), this brazing beingaccomplished at a first temperature. Braze joints 80,82 are brazed firstusing the above described insulator braze materials 100 for theinsulator-ferrule braze joint 82 and the insulator-lead braze joint 80.After brazing, the insulator 28 is securely joined to the ferrule 24 andthe lead 30 is securely joined to the insulator 28.

[0038] The next step for forming the feedthrough 20 calls for thebrazing of the capacitor 22 in the ferrule 24 using the capacitor brazematerials 102, these braze materials having different properties, suchas lower eutectic melting temperatures, than the insulator brazematerials 100 used in the first step. The capacitor receiving recess 52has positioned adjacent thereto an annular shaped capacitor preform (notshown in the figures) made of capacitor braze material 102. The annularshaped braze preform having a diameter such that is substantially thesame as the diameter of the capacitor receiving recess 52A. The portionof the lead 30 received in the capacitor passageway 74 is wrapped in athread-type preform (not shown in the figures) made of capacitor brazematerial 102. The capacitor braze material 102 is initially seated abovethe capacitor-ferrule braze joint 90 and capacitor-lead braze joint 92,and upon brazing, capacitor braze material 102 flows into the spacebetween the metallized external surface layer 78A of the of thecapacitor 22 and the interior sidewall 52B of the capacitor receivingrecess 52, thus forming the capacitor-ferrule braze joint 90. The meltedcapacitor braze material 102 also flows between the metallized internalsurface layer 76A of the capacitor passageway 74 and the lead 30, thusforming the capacitor-lead braze joint 92. The flow of the meltedcapacitor braze material 102 is due to capillary and wetting forces.

[0039] The second step of brazing calls for the brazing of thecapacitor-ferrule braze joint 90 and capacitor-lead braze joint 92, andthis brazing occurs at a second temperature lower than the brazingtemperatures of the first step, wherein the insulator-ferrule brazejoint 82 and insulator lead braze joint 80 were formed. This is becausethe capacitor braze material 102 has a lower melting or liquidustemperature than that of the insulator braze material 100. One of theadvantages with the brazing of the second step being done at a lowertemperature than the brazing in the first step is that the lowertemperature does not affect the hermetic seal formed by the previouslybrazed insulator-ferrule braze joint 82 and insulator lead braze joint80.

[0040] An example of the two step brazing process of the presentinvention follows. First, the insulator-ferrule braze joint 82 and theinsulator-lead braze joint 80 are formed by using, for example pure goldfor the insulator braze material 100, that melts at 1063 degreescentigrade. The method of brazing known to those skilled in the art.

[0041] Then, the capacitor-ferrule braze joint 90 and capacitor-leadbraze joint 92 are formed using a 72% silver 28% copper capacitor brazematerial 102 having a eutectic melting temperature of 780 degreescentigrade. The braze preforms made of the capacitor braze material 102for the capacitor-ferrule braze joint 90 and for the capacitor-leadbraze joint 92 are installed in the feedthrough 20 as previouslydescribed and the feedthrough 20 assembly is heated in a vacuum furnace(not shown) to a temperature exceeding the 780 degree centigradeeutectic melting point of the seventy-two percent silver andtwenty-eight percent copper capacitor braze material 102. Upon melting,the capacitor braze material 102 wets the interior sidewall 52B of thecapacitor receiving recess 52 and the metallized external surface layer78A of the exterior capacitor surface 78 and flows therebetween. Thecapacitor braze material 102 also wets the lead 30 and the metallizedinternal surface layer 76A of the internal surface 76 of the capacitorpassageway 74 and flows therebetween. After brazing, the feedthrough 20is then left to cool, and when cooled, the capacitor braze material 102cools and solidifies forming a robust metallurgical and electricalconnection, thus joining the capacitor 22 and the lead 30 and joiningthe capacitor 22 and the ferrule 24.

[0042] After the brazing process, the first set of capacitor plates 120is conductively coupled to the ferrule 24 and the second set of plates130 is conductively coupled to the lead 30. Also, after brazing, thelead 30 passes through the feedthrough 20 in a nonconductive manner.Thus, the solidified capacitor braze material 102 forms a robustmechanical and electrical connection directly from the exteriorcapacitor surface 78 of the capacitor 22 to the ferrule 24 and from theinternal surface 76 of the capacitor passageway 74 of the capacitor 22to the lead or pin 30. Further, after brazing, the feedthrough 20 ishermetically sealed. The feedthough 20 may then be joined to the housing32 after brazing is complete.

[0043] Thus the present invention provides a filter capacitorfeedthrough assembly 20 including an all braze arrangement whereincapacitor braze material 102 joins the capacitor 22 to the feedthroughpin or lead 30 and to the ferrule 24, and wherein insulator brazematerial 100 joins the insulator 28 to the pin or lead 30 and to theferrule 24. The braze arrangement and method according to the inventionhas a number of important distinctions and advantages over prior artassemblies and methods utilizing soldered joints. One difference is thetemperature levels at which the respective operations are performed andto which the resulting joints can be exposed subsequently before theyfail. Brazing may be defined as a group of joining processes whichproduces a coalescence of materials by heating them to a suitabletemperature and by using a filler metal having a liquidus above 448.9degrees centigrade and below the solidus of the base metal. Solderingmay be defined as a group of joining processes which producescoalescence of materials by heating them to a suitable temperature andusing a filler metal having a liquidus not exceeding 448.9 degreescentigrade and below the solidus of the base metal.

[0044] Another distinction involves how the bond is established.Adhesion is the primary mechanism in soldering, but in brazing, alloyingand diffusion are the principal means of establishing the bond. Thetemperature to which a brazed joint can be exposed after formation ishigher than the temperature to which a soldered joint can be exposed,because the solder can remelt at a lower temperature, threatening theintegrity of the joint.

[0045] Furthermore, in soldering only mechanical bonded joints areformed, whereas in brazing a metallurgical joint is formed. Moreover, insoldering fluxes are typically required, whereas in brazing the use offlux is optional. Finally, in soldering the heat is supplied by asoldering iron, ultrasonic devices, resistance, ovens, etc, whereas inbrazing the heat is supplied by a furnace, chemical reaction, inductiontorch, infrared, etc.

[0046] In the process of the invention, the brazing of the capacitor 22is conducted at a temperature above 780 degrees centigrade, well abovethe minimum temperature for brazing. The brazing operation is performedin a brazing furnace, whereas the soldering operation is performed in alower temperature oven. A flux is not used in the brazing process of theinvention. This is an advantage, because it eliminates a processing stepand avoids a cleaning operation and possible contamination of theimplantable medical device by residual flux material.

[0047] The fact that the brazed joint can be exposed to a highertemperature than can a soldered joint is another important advantage anddistinction of brazing. The feedthrough of the invention may beultimately welded to the case of an implantable medical device. Asoldered joint may be exposed to a temperature high enough to melt thesolder during the welding process, potentially causing the reflow of thesolder and even freeing part of the solder from the base metal. If thelatter were to happen, a “solder ball” could form which might fall fromthe feedthrough into the pacemaker or defibrillator, potentially causinga short circuit within the device if it touches any electroniccomponents.

[0048] In a second embodiment of the present invention, seen in FIG. 3,the ferrule 24 is provided with an internal lip 56 positioned betweenthe insulator receiving recess 50 and the capacitor recess 52. In thisembodiment the intermediate recess 54 has a diameter designated 54A thatis less than the diameters of the insulator receiving recess 50 andcapacitor receiving recess 52, and the insulator 28 does not contact thecapacitor 22 as is the case in the first embodiment of the presentinvention. During the two step brazing process, the braze materials maybe selected from the above described lists of braze materials andaccomplished in the manner described with respect to the firstembodiment.

[0049] In a third embodiment of the invention, shown in FIG. 4, thefeedthrough 190 is provided with a plurality of conductive leads 194,196that pass through a plurality of lead passageways 198, 200 defined inthe insulator 204. The insulator 204 is received in the insulatorreceiving recess 208 in the ferrule 206. The capacitor 212 is receivedin the capacitor receiving recess 210 in the ferrule 206. The insulator204 protrudes a distance into the capacitor recess 210 and contacts thecapacitor 212. In a manner substantially the same as the brazingprocesses and procedures fully described above for the first embodimentof the invention, the insulator 204 is brazed to the plurality of leads194,196 and to the ferrule 206 with an insulator braze material 215, andthe capacitor 212 is brazed to the ferrule 206 and to the plurality ofleads 194,196 with a capacitor braze material 217. The braze jointsbetween leads 194,196 and the insulator 204 and between the insulator204 and the ferrule 206 are indicated by reference numbers 214 and 216respectively and are made of the insulator braze material 215. Theinsulator braze material 215 and the capacitor braze material 217 may beembodied as the same insulator braze materials 100 and capacitor brazematerials 102 as described in the first embodiment of the presentinvention.

[0050] The feedthrough 200 may be mounted on a housing 218 that may bean implantable medical device such as the housing of a pacemaker ordefibrillator (not shown). A joint 219 is formed where the feedthrough200 is mounted to the housing 218, the manner of mounting and formingjoint 219 known to those skilled in the art.

[0051] The same two step brazing process as described in the firstembodiment is employed to braze the feedthrough of the third embodiment.

[0052] In particular, in the first step, the insulator braze materials215 for the insulator-lead braze joint 214 and the insulator-ferulebraze joint 216 may comprise:

[0053] pure gold;

[0054] gold alloys comprising at least one of tin, copper, silver,palladium, indium, titanium, niobium, vanadium, nickel, molybdenum,platinum;

[0055] silver;

[0056] silver alloys containing at least one of gallium, palladium, andaluminum; and

[0057] copper silver alloys that may contain tin, indium, palladium,nickel, gallium, palladium, and titanium.

[0058] The second step involves brazing the capacitor 212 to the ferrule206 and to the plurality of leads 194, 196. The capacitor 212 may bediscoidal in shape, and may be embodied to have a pair of capacitorpassageways 220 and 222 to receive leads 194 and 196 respectively. Ametallized external surface layer 224 is located about the circumferenceof the capacitor 212. The capacitor passageways 220 and 222 havemetallized internal surface layers 226 and 228 respectively. An annularbraze preform (not shown) made of capacitor braze material 217 ispositioned about the capacitor 212 and the thread type braze preforms(not shown) made of capacitor braze material 217 are threaded to theleads 194 and 196, respectfully. The braze preforms made of capacitorbraze material 217 are used to form the capacitor-ferrule braze joint270 and the capacitor-lead braze joint 272 respectively, and thecapacitor braze material 217 may be embodied to comprise the following:

[0059] seventy-two percent silver and twenty-eight percent copper;

[0060] copper and silver and at least one of the following elements:titanium, indium, gallium, palladium, platinum, nickel or tin, so longas they are compatible with the capacitor 22 termination materials;

[0061] silver-germanium alloys;

[0062] gold alloys; and

[0063] silver-palladium-gallium alloys so long as these materials arecompatible with capacitor termination materials.

[0064] As with the first embodiment, in the third embodiment theferrule-capacitor braze joint 270 and capacitor-lead braze joints 272may use a capacitor braze material 217 comprising seventy-two percentsilver and twenty-eight percent copper. The feedthrough 190 may then beassembled and heated in a vacuum furnace (not shown) to a temperatureexceeding the 780 degree Centigrade eutectic melting point of theseventy-two percent silver and twenty-eight percent copper braze. Uponmelting, the braze material wets the interior sidewall 274 of thecapacitor receiving recess 210 and the metallized external surface layerof the capacitor 276. After brazing the feedthrough 190 is then left tocool, the ferrule-capacitor braze joint 270 and capacitor-lead brazejoints 272 form a robust metallurgical and electrical connection, thusjoining the capacitor 212 to the ferrule 206 and joining the leads 194,196 to the capacitor.

[0065] The capacitor itself may have first and second sets of plates240, 242 respectively, separated by a dielectric material 244. The firstset of plates 240 contacts the ferrule 206 through the capacitor-ferrulebraze joint 270 and the second set of plates 242 contacts the leads194,196 through the capacitor-lead braze joints 272.

[0066] After the brazing process, the first set of capacitor plates 240is conductively coupled to the ferrule 206 and the second set of plates242 is conductively coupled to the leads 194,196. Thus, the solidifiedbraze forms a robust mechanical and electrical connection directly fromthe capacitor 212 to the ferrule 206 and from the capacitor 212 to theleads 194,196.

[0067] Also, the ferrule 206 has a chamfered annular internal surface230 that defines a gap space 252 when the insulator 204 and capacitor212 are positioned in the ferrule 206, as seen in FIG. 4. This gap space232 may fill partly with melted insulator braze material 215 during thebrazing process. Thus, the two step brazing process fully described inthe first embodiment may be employed in the third embodiment of thepresent invention.

[0068] Thus, the present invention provides a new way to installcapacitor filters in feedthrough devices. Although several embodimentsof the invention have been described herein, various modifications maybe made without departing from the scope of the invention. All of thesealternative embodiments are intended to be within the scope and spiritof the appended claims.

What is claimed:
 1. A feedthrough comprising: a lead; a ferrule defininga capacitor receiving recess and the ferrule also defining an insulatorreceiving recess; a capacitor disposed in the capacitor receivingrecess, the capacitor defining a capacitor passageway for the lead topass; an insulator disposed in the insulator receiving recess, theinsulator defining an insulator passageway for the lead to pass through;an insulator braze material for forming an insulator-ferrule braze jointand for forming an insulator-lead braze joint; and a capacitor brazematerial for forming a capacitor-ferrule braze joint and for forming acapacitor-lead braze joint, wherein the insulator braze material isdifferent than the capacitor braze material wherein and theinsulator-ferrule braze joint and the insulator-lead braze joint arebrazed before the capacitor-ferrule braze joint the capacitor-lead brazejoint are brazed.
 2. The feedthrough of claim 1 wherein the capacitorcomprises a first set of plates and comprises a second set of plates,and wherein the first set of plates is conductively coupled to theferrule by the capacitor braze material and the second set of plates isconductively coupled to the lead by way of the capacitor braze material,the first set of plates and the second set of plates for filteringelectromagnetic interference, and wherein the capacitor braze materialis selected from the group consisting of: seventy-two percent silver andtwenty-eight percent copper; copper and silver and one of the followingelements selected from the group consisting of: titanium, indium,gallium, palladium, platinum, nickel, and tin; silver-germanium alloys;gold alloys; silver-palladium-gallium alloys; and copper and silveralloys comprising at least one of the elements selected from the groupconsisting of titanium, indium, gallium, palladium, platinum, nickel andtin.
 3. The feedthrough of claim 1 wherein the capacitor braze materialused for the capacitor-ferrule braze joint and for the capacitor-leadbraze joint comprises seventy-two percent silver and twenty-eightpercent copper.
 4. The feedthrough of claim 1 wherein the capacitorbraze material used for the capacitor-ferrule braze joint and for thecapacitor-lead braze joint comprises copper and silver one of thefollowing elements selected from the group consisting of: titanium,indium, gallium, palladium, platinum, nickel, and tin.
 5. Thefeedthrough of claim 1 wherein the capacitor braze material for thecapacitor-ferrule braze joint and the capacitor-lead braze joint isselected from the group consisting of: silver-germanium alloys; goldalloys; silver-palladium-gallium alloys; and copper and silver alloyscomprising at least one of the elements selected from the groupconsisting of titanium, indium, gallium, palladium, platinum, nickel andtin.
 6. The feedthrough of claim 1 wherein the insulator braze materialfor the insulator-ferrule braze joint and the insulator-lead braze jointcomprises gold.
 7. The feedthrough of claim 1 wherein the insulatorbraze material for the insulator-ferrule braze joint and the insulatorlead braze joint is selected from the group consisting of: gold alloyscomprising at least one of the following selected from the groupconsisting of: tin, copper, silver, palladium, indium, titanium,niobium, vanadium, nickel, molybdenum, platinum; silver; silver alloyscomprising at least one of the following selected from the groupconsisting of: gallium, palladium, and aluminum; copper silver alloys;and copper silver alloys comprising at least one of the followingselected from the group consisting of: tin, indium, palladium, nickel,gallium, palladium, and titanium.
 8. The feedthrough of claim 2 whereinthe ferrule further comprises an interior sidewall for defining thecapacitor receiving recess, and the capacitor comprises an exteriorcapacitor surface provided with a metallized external surface layer, andthe capacitor further comprises an internal surface about the capacitorpassageway provided with a metallized internal surface layer, andwherein the capacitor braze material upon melting flows between theinterior sidewall of the ferrule and the metallized external surfacelayer of the capacitor and flows between the metallized internal surfacelayer of the capacitor passageway and the lead.
 9. The feedthrough ofclaim 8 further comprising a thread-type preform comprising capacitorbraze material that is wrapped about the lead so that during brazing thethread type preform melts and flows between the lead and the metallizedinternal surface layer of the capacitor passageway, and the externalsurface of the capacitor has positioned proximate thereto an annularshaped capacitor preform of capacitor braze material so that duringbrazing the annular shaped capacitor braze preform melts flows betweenthe interior sidewall of the ferrule and the metallized external surfacelayer of the capacitor passageway and the lead.
 10. The feedthrough ofclaim 1 wherein the insulator-ferrule braze joint and the insulator-leadbraze joint is brazed at first temperature and the capacitor-ferrulebraze joint and capacitor-lead braze is braze at a second temperature,the second temperature being less than the first temperature.
 11. Thefeedthrough of claim 10 wherein a thread-type preform wrapped around thelead prior to brazing and the annular shaped capacitor preform forpositioning proximate to the exterior capacitor surface compriseseventy-two percent silver and twenty-eight percent copper.
 12. Thefeedthrough of claim 1 wherein the insulator is positioned in theinsulator receiving recess and the capacitor is positioned in thecapacitor receiving recess such that they contact one another and thelead passes through the ferrule in a nonconductive manner.
 13. Thefeedthough of claim 12 wherein the ferrule is joined to an implantablemedical device comprising a housing having an interior, such that thelead passes from the interior of the housing to a location external tothe housing by way of the feedthrough in a nonconductive manner.
 14. Afeedthrough comprising; a lead; a ferrule defining an insulatorreceiving recess and an insulator disposed in the insulator receivingrecess, the insulator defining a passageway for the lead to passtherethrough, the insulator brazed to the ferrule brazed to the leadwith an insulator braze material; the ferrule further defining acapacitor receiving recess into which a capacitor is disposed, thecapacitor comprising capacitor exterior surface and defining a capacitorpassageway for the lead to pass therethrough; and a thread-type preformthreaded about the lead at the location where the lead is proximate thecapacitor passageway, and an annular capacitor preform positionedadjacent to the capacitor exterior surface, wherein the thread-typepreform and the capacitor preform are made of a capacitor braze materialand wherein the insulator braze material has a higher meltingtemperature than the capacitor braze material.
 15. The feedthrough ofclaim 14 wherein the capacitor braze material from which the thread-typepreform and the annular capacitor preform are made comprisingseventy-two percent silver and twenty-eight percent copper.
 16. Thefeedthrough of claim 14 wherein the thread-type preform and the annularcapacitor preform are made from a capacitor braze material comprisingcopper and silver at least one of the following materials selected fromthe group consisting of: titanium, indium, gallium, palladium, platinum,nickel, and tin.
 17. The feedthrough of claim 14 wherein the thread-typepreform and the capacitor preform are made from a capacitor brazematerial selected from the group consisting of: silver-germanium alloys,gold alloys, and silver-palladium-gallium alloys.
 18. The feedthrough ofclaim 14 where the capacitor braze material is selected from the groupconsisting of: seventy-two percent silver and twenty-eight percentcopper; copper and silver and at least one of the following selectedfrom the group: titanium, indium, gallium, palladium, platinum, nickel,and tin; and silver-germanium alloys, gold alloys, andsilver-palladium-gallium alloys.
 19. The feedthrough of claim 14 whereinthe insulator and the ferrule form an insulator-ferrule braze joint andthe insulator and the lead form an insulator-lead braze joint, and thecapacitor and the ferrule form a capacitor-ferrule braze joint and thecapacitor and the lead form a capacitor-lead braze joint, and whereinthe insulator braze material is used for brazing the insulator-ferrulebraze joint and the insulator-lead braze joint has a higher meltingtemperature than the capacitor braze material used for forming thecapacitor-ferrule braze joint and the capacitor-lead braze joint, theinsulator-ferrule braze joint and the insulator-lead braze joint areformed before the capacitor-ferrule braze joint and the capacitor-leadbraze joint are formed.
 20. A process of brazing a filter capacitor in afeedthrough device comprising the acts of: providing a ferrule, theferrule defining a capacitor receiving recess; disposing a capacitor inthe capacitor receiving recess; providing the capacitor with apassageway, and a metallized external surface about the capacitor and ametallized internal surface about the defined passageway, the capacitorpassageway for allowing a lead to pass therethrough; providing acapacitor braze material between the ferrule and the metallized externalsurface of the capacitor; providing the capacitor braze material betweenthe lead and the metallized internal surface of the capacitor; brazingthe capacitor's metallized external surface to the ferrule forming acapacitor-ferrule braze joint; and brazing the capacitor's metallizedinternal surface to the lead forming a capacitor-lead braze joint. 21.The process of claim 20 wherein the capacitor braze material comprisesseventy-two percent silver and twenty-eight percent copper.
 22. Theprocess of claim 20 wherein the capacitor braze material comprisescopper and silver and at least one of the following materials selectedfrom the group consisting of: titanium, indium, gallium, palladium,platinum, nickel, and tin.
 23. The process of claim 20 wherein thecapacitor braze material comprises silver-germanium alloys, gold alloys,and silver-palladium-gallium alloys.
 24. The process of claim 20 whereinthe brazing further comprises the acts of: wrapping a thread-typepreform about the lead; positioning adjacent to the capacitor'smetallized external surface an annular capacitor preform, and whereinthe thread-type preform and annular capacitor preform comprise thecapacitor braze material that comprises seventy-two percent silver andtwenty-eight percent copper; placing the feedthrough in a vacuumfurnace; and heating the vacuum furnace to a temperature exceeding sevenhundred eighty degrees centigrade causing the capacitor braze materialto melt and flow between the metallized external surface of thecapacitor and the metallized internal surface of the capacitor; andcooling the feedthrough.
 25. The process according to claim 20 whereinthe acts of brazing further comprises: selecting the capacitor brazematerial from the group consisting of: seventy-two percent silver andtwenty-eight percent copper; titanium, indium, gallium, palladium,platinum, nickel, and tin; and silver-germanium alloys,silver-palladium-gallium alloys.
 26. The process of claim 25 furthercomprising the acts of: selecting a capacitor braze material for thethread-type preform and for the annular capacitor preform and wrappingthe thread-type preform about the lead and positioning the annularcapacitor preform adjacent to the capacitor; placing the feedthrough ina vacuum furnace; heating a vacuum furnace to a temperature exceedingthe liquidus temperature of the selected capacitor braze materialcausing the braze to melt and seep into the metallized external surfaceof the capacitor and the metallized internal surface of the capacitorpassageway; and cooling the feedthrough.
 27. A process of brazing aninsulator and a filter capacitor in a feedthrough device comprising theacts of: providing a ferrule; defining a capacitor receiving recess andan insulator receiving recess in the ferrule; disposing an insulator inthe insulator receiving recess; defining an insulator passageway in theinsulator, the insulator passageway for receiving a lead therethroughand disposing a lead therethrough; disposing a capacitor comprising ametallized external surface layer in the capacitor receiving recess, thecapacitor further defining a capacitor passageway for allowing the leadto pass therethrough, the capacitor passageway comprising a metallizedinternal surface layer; establishing an insulator-ferrule braze jointwhere the insulator meets the ferrule and establishing an insulator-leadbraze joint where the insulator meets the lead; providing an insulatorbraze material at the insulator-ferrule braze joint and at theinsulator-lead braze joint; establishing a capacitor-ferrule braze jointwhere the capacitor meets the ferrule and establishing a capacitor-leadbraze joint where the capacitor meets the lead; providing a capacitorbraze material at the capacitor-ferrule braze joint and at thecapacitor-lead braze joint, the insulator braze material having a highermelting temperature than the capacitor braze material; first brazing theinsulator to the ferrule and brazing the insulator to the lead at afirst temperature using the insulator braze material; and next brazingthe capacitor to the ferrule and brazing the capacitor to the lead tothe lead using the capacitor braze material at a second temperature thatis lower than the first temperature.
 28. The process according to claim27 further comprising the acts of: positioning an annular shapedcapacitor preform adjacent to the metallized external surface layer ofthe capacitor and wrapping a thread-type preform about the lead, theannular shaped capacitor and the thread-type preform comprise capacitorbraze material selected from the group consisting of: seventy-twopercent silver and twenty-eight percent copper; titanium, indium,gallium, palladium, platinum, nickel, and tin; and silver-germaniumalloys, ninety nine point ninety nine percent pure gold, gold alloys,and silver-palladium-gallium alloys.
 29. The process of claim 28 furthercomprising the acts of: selecting a capacitor braze material for thethread-type preform and for the annular capacitor preform; placing thefeedthrough in a vacuum furnace; heating a vacuum furnace to atemperature exceeding eutectic melting temperature of the selectedcapacitor braze material causing the capacitor braze material to meltand flow between the interior sidewall of the ferrule and the metallizedexternal surface layer of the capacitor causing the capacitor brazematerial to flow between the metallized internal surface layer of thecapacitor passageway and the lead; and cooling the feedthrough.
 30. Theprocess of claim 28 further comprising the acts of: selecting theseventy-two percent silver and twenty-eight percent copper brazematerial for the thread-type preform; and selecting the seventy-twopercent silver and twenty-eight percent copper a braze for the capacitorpreform.
 31. The process of claim 27 wherein the insulator brazematerial for the insulator-ferrule braze joint and insulator-lead brazejoint is selected from the group consisting of: gold alloys comprisingat least one of the following selected from the group consisting of:tin, copper, silver, palladium, indium, titanium, niobium, vanadium,nickel, molybdenum, platinum; silver; silver alloys comprising at leastone of the following selected from the group consisting of: gallium,palladium, and aluminum; copper silver alloys; and copper silver alloyscomprising at least one of the following selected from the groupconsisting of: tin, indium, palladium, nickel, gallium, palladium, andtitanium.
 32. A feedthrough comprising: a plurality of leads; a ferruledefining a capacitor receiving recess and the ferrule also defining aninsulator receiving recess; a capacitor disposed in the capacitorreceiving recess, the capacitor defining a plurality of capacitorpassageway for the plurality of leads to pass; an insulator disposed inthe insulator receiving recess, the insulator defining a plurality ofinsulator passageways for the lead to pass through; an insulator brazematerial for forming an insulator-ferrule braze joint and for forming aninsulator-lead braze joint; and a capacitor braze material for forming acapacitor-ferrule braze joint and for forming a capacitor-lead brazejoint, wherein the insulator braze material is different than thecapacitor braze material wherein and the insulator-ferrule braze jointand the insulator-lead braze joint are brazed before thecapacitor-ferrule braze joint the capacitor-lead braze joint are brazed.